Modern integrated circuits may have multiple power supply voltages. In particular, modern integrated circuits may have one power supply voltage used to power most of the internal circuitry and another to power the output circuitry. Typically, the output circuitry is powered by a higher power supply voltage than the internal circuitry. This allows the output circuitry to produce output voltage swings that are compatible with a variety of logic families. It also helps ensure that the output voltage swings are large enough to be received even in the presence of significant external noise.
To increase switching speed and to reduce power consumption, the internal circuitry of an integrated circuit may utilize so-called low voltage field-effect transistors (FETs) that are designed to work well with the lower (internal) power supply voltage. However, these low voltage FETs may suffer from degraded reliability the longer they are exposed to the higher voltages that may be present in output circuitry.